This research project is involved with defining both the enzymatic sites controlled in liver by homones and the mechanisms by which hormones regulate these sites. Attention is focused on the role of hormonal regulation of mitochondrial pyruvate carboxylation as it relates to gluconeogenesis and on the role of protein phosphorylation in the control of cytoplasmic enzymes such as phosphorylase, glycogen synthase and pyruvate kinase. Isolated liver cells are used as experimental material, and the hormones under study are glucagon, catecholamines, angiotensin and vasopressin.